Ball mandrel



F. SASSAK BALL MANDREL Nov. 5, 1968 2 Sheets-Sheet 1 Filed April 2]., 1966 INVENTOR. FRANK SASSAK ATTORNEYS Nov. 5, 1968 F. SASSAK 3,408,851

BALL MANDREL Filed April 21, 1966 2 Sheets-Sheet 2 INVENTOR. FRANK SASSAK TTORNEYS United States Pate 3,408,851 a BALL MANDREL Frank Sassak, Dearborn, Mich., assignor to Bend-Rite,

Inc-, Detroit, Mich., a corporation of Michigan I Filed Apr. 21, 1966, Ser. No.544,220

' 3 Claims. (Cl. 72-466) ABSTRACT OF THE DISCLOSURE members.

The present invention relates to an, improved ball mandrel for use in the bending of tubular parts, for example pipe fittings and the like, on a standard horizontal bending machine, or possibly a bending press or other equivalent equipment. The operation involves a draw bending of the tube, as supported from within by the mandrel, about an arcuate bending form or tool; and the improved mandrel makes possible the production of extremely sharp bends without wrinkling, marring or distortion of the tube in the process.

It is a general object of the invention to provide a ball mandrel which is of great strength as compared with those presently in industrial use, and is not subject to distinct size limitations inhering in most of the latter, particularly in the forming of tubing of small OD. On the other hand, the improved mandrel is also free of limitation as to use in the bending of much larger tubes.

For example, a 1-D bend is commonly recognized by the industry as being a minimum practical bend; however, a mandrel in accordance with the present improvement may well be designed, manufactured and used in the making of /z-'D bends, although necessarily being of less strength than a mandrel designed for a larger minimum radius, since the strength and minimum bend radius are in general proportional. Lack of sufficient strength presents a great problem of breakage of ball mandrels in the tube bending industry, and the improved mandrel of the present invention is believed to be a solution of this problem.

More specifically, the inventon provides a ball mandrel which is typically composed of three strong and strongly articulated components. These are, in progression from rear to front of the mandrel, a cylindrical mandrel body have a slightly, quasi-spherical forward nose; an intermediate ball member, also of quasi-spherical external contour, being truncated at its exial ends, although not necessarily in uniform axial extent, for a reason to appear; and an outer or forward ball component, about which the ID of the tube slides and is firmly ironed as bending proceeds, in the normal manner of operation of horizontal, mandrel-assisted draw bending equipment.

These mandrel parts are successively articulated in a novel and improved manner to resist separation and/or breakage; and in the illustrated embodiments of the invention they are positively restrained to swing in a single plane. However, such restraining means may be eliminated or modified if a universal action is desired for the production of compound or multidirectionally bent tubes. While, as indicated above, a three-section ball mandrel is herein shown and described, it is to be understood that a 3,408,851 .Patented Nov. 5, 1968 "ice . L longer unit is contemplated by the invention, for example one embodying two or more intermediate ball components.-

The-invention is-xnot to be considered as particularly limitedin reference to the specific manner and means bywhich the body, intermediate and outer ball parts are positively linked for pivotal action. Thus, one basic embodiment of the mandrel employs an intermediate ball member which is socketed .i'na forward," partial depth bore-or'r'ee cess of the rear body member,-as by means of an annular series of bearing balls acting against and axially restraim ing a quasi-ball shaped rear extension of the intermediate mandrel member; and a similar forward mandrel stem extension is similarly articulated at its rear in similar for ward socket provisions of the intermediate member. It is contemplated in such type of embodiment that a number of arcuate segments of round wire stock in a circumferential succession may be substituted for the bearing ball series. In this adaptation a sliding but non-rolling bearing action would be present.

In other adaptations of the invention, the axial restraint of the intermediate and outer or forward ball parts, at their respective quasi-spherical rear stem extensions, is

accomplished by using non-roller type means in which the stem extension has pivotally socketed reception. In a typical such unit, a pair of segmental, semi-circular members, as mounted in encircling relation to the stem extension, are seated in an annular groove machined in the forward socket recess of the respective body and intermediate ball members. The restraining members are each ground or otherwise machined to afford concave socketing surfaces for mating and socketing engagement with the bearing surface of the stem.

In a slight modification of this second alternative type of axial bearing restraint, the semi-circular members are simply held in place in a recess by a snap ring; while in another adaptation the restraintis=accomplished by split nut means, in the form of a pair of generally semi-circular nut members, against the concave-contoured bearing surfaces of which the stein extension engages pivotally.

Still another alternative construction of the improved mandrel, which is particularly well suited for the produc tion of small size bends, dispenses with the use of separate bearing and restraining elements. It contemplates the machining of the rear and intermediate mandrel members to provide coaxial,.concave restraining and bearing surfaces directly on the interior of the forward socket bore or recess of the respective parts; and the stem extensions of the latter are specially formed to provide radially extending bearing and restraining formations or arms of externally rounded shape for coaction with such socket surfaces.

Assembly of .the rounded stem arms in operative pivotal relation to the machined socket surfaces is made possible by milling radial slots to subdivide those surfaces into circumferentially spaced bearing seat portions which face inwardly about the socket recesses. Hence the stem arm formations may be inserted into the spaces between seat portions, after which the stem extension is rotated about its axis to bring its arm portions into registering and mating engagement with and behind the respective socket seat portions. In an embodiment of this character, means of one sort or another are of course necessary to prevent further relative rotation of the coupled parts about the axes thereof.

It will therefore be appreciated that, within the broad objective of the invention to provide a very rugged and very strongly articulated ball mandrel, the specific character of the articulating, pivoting or swiveling means may vary quite a bit; and those skilled in the art will most likely 'per ceive still othei' alternative equivalents 4 for the in As indicated above mandrel 10 is typically composed In further specific accordance with the invention, it is desirable to form the forward socket bore of the intermediate ball member onlan axis'cantedor'oifsct some what relative to astraight line axis of'the'mandrel (including its cylindrical body) through the pivot axis of the intermediate memberkThis-perr'nits a more pronounced swing 'of the socketed intermediate and forward parts relative to the, mandrel body and one another than would be thecase .if the bore'iinrquestion' were-exactly coaxial witlrtthe axis'of themandrelas a whole. It hasthe same effect as a reduction in thestem diameter wouldhave', but without a diminution of strength which would accompany such reduction of the stern diameter.

As indicated above, the mandrel parts are preferably, although not necessarily in all instances, positively restrained for pivotal movement in a single plane. In accordance with the present improvement this is accomplished by'the use of a forward restraining pin extending transversely through each ofthe body and intermediate mandrel parts at their respective socket bores. The respective intermediate-and forward mandrel parts are disposed in axial engagement with such pins, as at transverse grooves in their rear stem extensions, in a manner to maintain a uni-planar action in the bending operation.

The foregoing as Well as other objects will become more apparent as this description proceeds, especially when considered in connection with the accompanyin drawings illustrating the' 'invention, wherein: FIG. 1 is a view partially broken away, in longitudinal section on a plane through the longitudinal axis of the improved mandrel, in accordance with'one embodiment thereof, as along line 1-1 of FIG. 2;

FIG. 2 is a sectional view in' 90" relation to FIG. 1, i.e., along line 2-2 of that figure;

FIG. 3 is a fragmentary view, in section corresponding to FIG. 1, showing the rear body member of a mandrel equipped with bearing and restraining provisions" of a type alternative to those of FIG. 1 and 2;

FIG. 4 is a fragmentary section similar to FIG. 3, but with further modified bearing and restraining means;

FIG. 5 is a fragmentary sectional view similar to FIGS. 3 and 4, in which the means in question is represented by a still further alternative, in the form of a segmented or split nut;

FIG. 6 is a fragmentary view, partially broken away, of another basic modification contemplated by the invention, in which bearing and restraining formations are machined directly upon the 'pivotally articulated parts;

FIG. 7 is a view in transverse vertical section on line 77 of FIG. 6;

FIGS. 8 and 9 are, respectively, rear and side elevational views showing the manner of specially forming the stem extensions ,of the socketed parts, i.e., the intermediate and forward v mandrel members, FIG. 8 being as viewed from the line 8-8 of FIG. 9; and

FIG. 10 is a fragmentary view in longitudinal cross section corresponding to FIGS.=1 and 3-5, showing a typical positional relationship of the mandrel parts to one another, as employed in conjunction with components of a draw bending machine, in the forming of a tube to a 1-D bend, or sharper. FIGS; 1 and 2 of thedrawings represent one of five herein-illustrated embodiments or adaptations of the in vention, this form being generally designated by the reference numeral 10. Simply for the sake of illustration and comparison, mandrel 10 may be taken as being designed for the forming to a 1-D bend'of a tube having a 5 /2 inch OD and a wall thickness of 0.065 inch. As understood in the industry, a 1-D bend is one in which the distance between the legs of a 180 tube bend equals the outer diameter of the tube. A /2-D bend would have the distance one-half of the OD.

hardened steel, although the number may be greater, as indicated above. Such parts are a rear or body member 11, an intermediate ball memberor section 12 and a forward or outer ball member 13 i Body 11 is appropriately'elongated in axial length and is provided .withai forward nose portion 14 having a spherical diameter of .slight. axia1 extent Radially inwardly of this nose the body-.part.11 .is machined on the axis thereof to provide a partial depth center socket bore or recess 15, whichwill'behereinafter referred to in detail; and the *rearof mandrel body llalsohas an axial bore 16 for the fixed reception of an appropriate elongated anchoring rod (not shown), in a manner typical of ball mandrel construction and usage.

The second or intermediate part 12 of the mandrelQlO is of quasi-spherical shape and truncated at its axial ends along non-parallel planes. Like the body 11, member 12 is formed to provide a forwardly opening partial bore 17, but in this case the axis of recess 17 is offset or canted at an angle A, amounting to about 15, to a horizontal plane (FIG. 1) through the pivotal axis (to be described) of ball member 12, and the axis of the cylindrical rear body part 11, for a purpose to be referredto. As indicated in FIG. 1, this tends to diminish the sectional thickness of part 12 across a portion thereof adjoining bore 17, but there is still ample metal for desired strength. 1

Intermediate member 12 is further formed to provide an integral, rearwardly projecting stem or extension 18, which extension connects to a forward .ball portion 19, proper, of the intermediate-part through a neck portion 20, the diameter of which affords great inherent strength to resist breakage. The stem extension 18 has a semi-cylindrical outer bearing and retaining surface 22 and terminates at its rear in a transversely and diametrically extending fiat surface 23, which is centrally interrupted by a semi-circular diametral recess 24.

This recess mates rearwardly with a transverse restraint pin 26 disposed in aligned radial bores 27 through the nose zone 14 of mandrel body 11, and the pin is held in place by end plugs 28 driven with a force fit into counterbores of the cross bores 27. The location of the restraint pin 26 is such that it extends diametrically across the forward body bore 15, where it is engaged matingly by'the rear transverse recess 24 of intermediate ball member 12, thus to limit the latter for swing in a single plane relative to body 11. t

Pin 26 represents the pivotal axis of mandrel part 12, and this axis is also the centerof the quasi-spherical nose surface 14 of body part 11. a

In accordance with the embodiment 10 of FIGS. 1 and 2,.the bore 15 of body member 11 is machined in a trans verse radial plane to provide an internal annular groove 30; and an annular series, of appropriately hard bearing balls 31, in a substantially full 360 complement, are disposed between groove 30 and the convexly arcuate bearing andrestraining surface 22 of the stem 18 of-intermediate ball mandrel member 12. v The placement of the balls 31 may be made prior to the placement of the transverse restraint pin 26, with the rear surface 23 of the extension abutting the bottomof body member groove 15. In the alternative, and also with the pin :26 removed,the balls may be loaded through the pinhole, with perhaps a slight adjoining groove being provided to accommodate balls of certain sizes. Other modes of-loading the bearing elements will suggest themselves to those skilled in the art. v

The third basic component of the mandrel 10, i.e., the outer or-forward ball member 13, is of-quasi-spherical shape presenting a flat transverse forward surface 33.'Like the intermediate member 12, ball member 13 has arearwardly-projecting neck 34 connecting the same with a semi-spherical stem extension 35 presenting a continuous arcuate bearing surface 36.

It will be noted that both of the members 11 and 12 are formed, just outwardly of the respective extension necks 20, 34 thereof, with annular fiat and circumferentially extending surfaces 38, against which similar forward annular surfaces 39 of the next rearward mandrel part may engage to limit fiexure of the mandrel 10, for example when one of the parts 12 or 13 is in its most extremely turned position, as depicted in FIG. of the drawings.

As in the case of the intermediate mandrel member 12, the forward member 13 has a transverse arcuate recess 40 in its rear surface for restraining engagement With a transverse pin 41 of part 12 to limit its Swing to a single plane about the axis of the pin. That axis also centers the quasi-spherical mandrel surface 42 of part 13. Ball member 32 has its axial restraint and pivotal hearing at the surface 36 thereof through the agency of a series of balls 42, positioned and operating identically to the balls 31 which articulate intermediate member 12 to body member 11. FIG. 2 shows that the restraint pin 41 for forward mandrel part 32 is axially held in place by force fitted end plugs 44.

It is to be understood that the alternative mandrel constructions illustrated in FIGS. 3, 4, 5 and 6 through 9 are, other than in their respective specific bearing and restraining provisions (to be described), contemplated as being provided with structural features corresponding to those referred to in connection with the mandrel embodiment 10 of FIGS. 1 and 2; and the action of these modified m-andrels is the same asis depicted in FIG. 10.

Specifically, in any mandrel having more than one intermediate ball member 12, the forward socket bore of each should be canted at the approximate offset shown in FIG. 1.

Referring now to FIG. 10, as therein shown a typical tube T is being progressively draw-bent, using the mandrel 10 in conjunction with a typical draw-bending form or tool 46 and clamping die members 47 and 47 of a conventional horizontal tube bending machine. It is seen that the partially spherical surfaces of the body, intermediate and forward parts 11, 12, 13 of the mandrel 10 provide for a smooth internal bending support of the tube T, ironing the wall of the latter in a continuous manner. It is also to be seen that the 15 offsetting of the forward bore 17 of the intermediate member (or members) 12 enables considerably greater swing of the latter and forward part 13, in reference to the body member 11, than would be the case if recess 17 were coaxial with the pivotal axis at the restraint pin 26. The quasi-spherical external surface 32 of intermediate ball member 12 is necessarily of non-uniform axial extent about its perimeter, but still has efficient ironing action at both of its smaller, intermediate and larger width portions on the internal wall of tube T as the latter draws about mandrel 10 in the usual manner.

As mentioned above, in lieu of steel ball bearings 31 and 43, the mandrel 10 may employ an annular series of arcuate, hardened sections of round steel wire stock, these sections providing a sliding bearing for the external surface 32 of the ball member 12. However, in most instances, the use of ball bearings is to be preferred.

In the embodiment of the invention illustrated in FIG. 3, the mandrel, generally designated by the reference numeral 48, employs bearing and axial restraint means of a non-rotary type. Such means is shown in the form of a pair of approximately semi-circularly segmented ring parts 49, 50, each ground or otherwise machined to provide an internally facing, concave bearing and restraint surface 51, which mates with the quasi-spherical surface 22 of the stem extension of the next preceding mandrel part, in this case the extension 18 of the intermediate ball member 12. The restraint members 49, 50 are located in an annular groove 52 machined radially in the bore 15 of the rear body part 11. This mode of connection is repeated at the articulation of the other members 12 and 13, and it affords bers to one 'another.

The embodiment of FIG. 4, generally designated 54, differs but slightly from that of FIG. 3, in that the segmental, generally circular restraining members, here designated 55 and 56, are axially abutted against an annular shoulder 57 formed in the body member bore 15, being then held in place by a snap ring 58. This embodiment may afford a somewhat lessened cost of production and assembly, as compared with that of FIG. 3.

In FIG. 5 a further modified mandrel construction, generally designated 60, is shown. In this instance the intermediate stem extension 18 is journaled and held in place by means of a split nut, including generally semicircular parts 61 and 62 which are ground or otherwise machined to afford'concave bearing and restraining surfaces at 63. Parts 61, 62 are externally threaded for engagement with threading 64 of the recess 15, and, as mat ingly fitted onto the extension 18, are threadingly rotated in place.

The next modified embodiment of the invention, generally designated by the reference numeral 66, which is shown in FIGS. 6, 7, 8 and 9, differs rather markedly from the embodiment of FIGS. 1 and 2, 3, 4 and S, and thus indicates the diversity of available ways in which a strong restraining articulation of the mandrel sections may be effected. In this case the coupling action is effected solely by means of-integral mated formations on the respective coupled mandrel members, rather than by separate means.

Thus, the rearbody member 11 of mandrel 66 (and the same is true of the intermediate member) has its forward recess or bore 15 internally machined, using a suitably shaped rotary cutter, to provide adjacent the forward portion of the recess an annular, quasi-spherically shaped, concave surface. This surface is then subdivided by a number of equally spaced radial cuts 68 (shown in FIG. 4 as four in number), to provide four bearing seat portions 69 extending radially about bore 15 and in equally spaced circumferential relation to one another. Each of these portions thus presents its own internally facing, concave and circumferentially arcuate bearing and restraining seat surface 70. v

In reference to the stem extension 18 of the intermediate mandrel member 12 (and this is also true of the corresponding extension of the forward part 13), this is specially formed in the mannerbest illustrated in FIGS. 8 and 9. That is, it is shaped in any appropriate manner to provide convexly arcuate external members 72 of quasispherical contour which extend radially outward thereof at a suitable number of equally spaced points, shown as four, each member presenting its own external bearing and restraining surface 73.

The circumferential Width of the members or projections 72 is sufficiently small to permit the ready axial entry of the same into the spaces 68 separating the internal bearing elements or portions 69 of the bore 15 of man-' drel body 11; and upon such positioning of the modified stern extension 18, it is rotated 45 (in the case of the four element embodiment of FIG. 7) to position the bearing projections 72 directly behind the respective recess bearing portions 69.

As thus positioned, the restraint pin 26 is put in place, being engaged in a transverse, generally semi-cylindrical recess 75 in the otherwise fiat rear face 76 of the stem extension. This not only confines the articulated member 12 for swing in a single plane, but also prevents rotation of its stern extension 18 about its own axis from the proper bearing and restraint position. As indicated above, the interlocked embodiment of mandrel 66, shown in FIGS. 6-9, has special utility in the formation of relatively small bends.

It will be appreciated from the above that the invention provides an improved ball mandrel for draw-bending metal tubes which includes a plurality of specially shaped body and ball me'mbersfpivotally articulated in an improved manner to one another in an axial succession, in which the'articulation is effected through the agency of special recess and extension formations on the respective members. The-"extension of one member is'received well within the recess ofthe adjacent member, which recess is of substantial bore size and receives the extensionof said'one member with substantial radial clearance, thus affording-a relatively -wide'pivotal swing of the members relative to one another about a pivotal axis located well within the mouth of the recess-bearin'g-member; and improved bearing means areprovided on the extension and within the recess to strongly prevent axial separation of the members from one another.

What I claim as my invention is: V

1. A ball mandrel comprising a plurality of pivotally articulated members including an axially rearward body member and a further ball member, directly forward of the body member, said body member being of generally cylindrical cross section and having a forwardly opening recess at the forward axial end thereof, said further member having an integral, rearwardly projecting extension presenting bearing and restraining means for that member disposed in the recess of the body member, said recess being provided with bearing and restraining means facing inwardly thereof for pivot-affording engagement with the bearing and restraining means of said extension of said further member, the respective bearing and restraining means acting to prevent axial separation of said members from one another while affording a substantial arc of relative swing of said members in a plane including the axis of said body member, said bearing and restraining means of said body member comprising an annular series of rotatable bearing elements in pivotal engagement with'the bearing and restraining means of said extension of said further member. v I I I 2, A ball mandrel comprising a plurality of pivotally articulated members, including a rear body member, at least one intermediate ball member and a further member directly forwardly of said intermediate member, said body member being of generally cylindrical cross section and having a forwardly opening recess at the forward axial end thereof, said intermediate member being in part of quasi-spherical shape but axially truncated in part at its forward and rear ends, said further member being in part quasi-cylindrical .in shape but axially truncated in part on at least its rear end, said intermediate member having a recess generally similar to that of said body member at its forward end, said intermediate and further members each having an integral extension projecting rearwardly .8 recesses each being provided with bearingand restraining means facing inwardly thereof for engagement' with the bearing and restraining means of said respective extensions to pivotally articulate said body, intermediate and further -members and prevent separation o'f the latter from one another, said bearing and restraining'm'eans' of each of said body and intermediate members comprising an annular series of rotatable bearing elements in pivotal engagement with the bearing and restraining means of said extension of 'said further member.

3; A ball mandrel comprising a plurality of pivotally articulated members, including a rear body member, at least one intermediate ball member and afurther member directly forwardly of said intermediate member, said body! member being of generally cylindrical cross section and having a forwardly opening recess at the forward axial end thereof, said intermediate member being in part of quasi-spherical shape but axially truncated in part 'at its forward and rear ends, said further member being in part quasi-cylindrical in shape but axially truncated in part on at least its rear end, said intermediate member having a recess generally similar to that of said body member, at its forward end, said intermediate and further members each having an integral extension projecting re arwardly of the rear truncated part thereof and presenting bearing and restraining means for said respective intermediate and further members which are disposed in the respective recesses of the body and intermediate members, said recesses each being provided with bearing and restraining means facing inwardly thereof, for engagement with the bearing and restraining means of said respective extensions' to pivotally articulate said body, intermediate and further members and prevent separation of the latter from one another, at least one of said body and intermediate members having means within the recess thereof to limit relative swing thereof to a single plane, said last named means comprising a pin extending through said recess on the pivotal axis of said relative swing, said bearing and restraining means of each of said body. and intermediate members comprising an annular series of rot a table bearing elements in pivotal engagement withthe bearing and restraining means of said extension of said further member. 1. References Cited ,1. a

UNITED STATES PATENTS 812,258 2/1906 Brinkman "7 2 46 3,190,106 6/l965 Spates 72 466 3,286,503 11/1966 Garrett 72-4 6 50 FOREIGN PATENTS 700,370 12/1953 Great Britain.

CHARLES W. LANHAM, Primary Examiner.

L. A. LARSON, Assistant Examiner. 

